// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
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package org.objectweb.asm.tree.analysis;

import java.util.ArrayList;
import java.util.List;
import org.objectweb.asm.tree.JumpInsnNode;
import org.objectweb.asm.tree.LabelNode;

/**
 * A method subroutine (corresponds to a JSR instruction).
 *
 * @author Eric Bruneton
 */
final class Subroutine {

	/** The start of this subroutine. */
	final LabelNode start;

	/**
	 * The local variables that are read or written by this subroutine. The i-th element is true if and only if the local variable at index i is read or written by this subroutine.
	 */
	final boolean[] localsUsed;

	/** The JSR instructions that jump to this subroutine. */
	final List<JumpInsnNode> callers;

	/**
	 * Constructs a new {@link Subroutine}.
	 *
	 * @param start
	 *          the start of this subroutine.
	 * @param maxLocals
	 *          the local variables that are read or written by this subroutine.
	 * @param caller
	 *          a JSR instruction that jump to this subroutine.
	 */
	Subroutine(final LabelNode start, final int maxLocals, final JumpInsnNode caller) {
		this.start = start;
		this.localsUsed = new boolean[maxLocals];
		this.callers = new ArrayList<>();
		callers.add(caller);
	}

	/**
	 * Constructs a copy of the given {@link Subroutine}.
	 *
	 * @param subroutine
	 *          the subroutine to copy.
	 */
	Subroutine(final Subroutine subroutine) {
		this.start = subroutine.start;
		this.localsUsed = new boolean[subroutine.localsUsed.length];
		this.callers = new ArrayList<>(subroutine.callers);
		System.arraycopy(subroutine.localsUsed, 0, this.localsUsed, 0, subroutine.localsUsed.length);
	}

	/**
	 * Merges the given subroutine into this subroutine. The local variables read or written by the given subroutine are marked as read or written by this one, and the callers of the given subroutine are added as callers of this one (if both have the same start).
	 *
	 * @param subroutine
	 *          another subroutine. This subroutine is left unchanged by this method.
	 * @return whether this subroutine has been modified by this method.
	 */
	public boolean merge(final Subroutine subroutine) {
		boolean changed = false;
		for (int i = 0; i < localsUsed.length; ++i) {
			if (subroutine.localsUsed[i] && !localsUsed[i]) {
				localsUsed[i] = true;
				changed = true;
			}
		}
		if (subroutine.start == start) {
			for (int i = 0; i < subroutine.callers.size(); ++i) {
				JumpInsnNode caller = subroutine.callers.get(i);
				if (!callers.contains(caller)) {
					callers.add(caller);
					changed = true;
				}
			}
		}
		return changed;
	}
}
